WASHINGTON (CNN) -- The International Committee of the Red Cross gathered "credible" reports about U.S. personnel at the Guantanamo Bay naval base disrespecting the Quran and raised the issue with the Pentagon several times, a group spokesman said Thursday.

Simon Schorno said the allegations were made by detainees to Red Cross representatives who visited the detention facility throughout 2002 and 2003.

State Department spokesman Richard Boucher said Thursday the Pentagon in 2003 issued strict guidelines on how U.S. personnel should handle the Quran.

Schorno said the Red Cross heard no more allegations about mishandling of the Quran after the guidelines were issued.

Boucher said the United States works closely with the Red Cross and acknowledged the group "had heard some concerns about the handling of Qurans, which it shared with the U.S."

But he said actions taken in respect of detainees' religious practices at Guantanamo include providing them with Qurans, indicating the direction to Mecca, providing the call to prayer and serving meals according to Muslim customs.

"We have very extensive guidelines about how Qurans are to be handled, who they're to be handled by, the wearing of gloves, how they're to be moved and transported, in order to ensure that no such concerns will arise," Boucher said.

Schorno did not provide specific instances of alleged desecration, instead addressing only to the general issue of disrespecting the Muslim holy book.

"The fact that ICRC documented these allegations, documented them and formalized them, I think makes a difference," Schorno said. "We researched them and found they were credible allegations."

Although Red Cross employees did not personally witness any mishandling of Qurans, Schorno said, they documented and corroborated enough reports from detainees to share them with Pentagon and Guantanamo officials in confidential reports.

Schorno said the Red Cross would not have raised the issue if it had been an isolated incident, but he would not offer specifics about the number of complaints.

"The very fact that we brought up the issue speaks for itself," he said. "We don't make such reports for minor problems."

U.S. officials have often downplayed such complaints about Quran desecration because they came from detainees.

Teams of Red Cross representatives have been making six-week visits to the U.S. detainee camp in Cuba every three months since 2002.

A Red Cross team is currently on the ground at Guantanamo, Schorno said.

A recent Newsweek magazine article alleged that U.S. investigators had concluded that U.S. interrogators at Guantanamo Bay desecrated the Quran, in one instance by flushing the Muslim holy book down a toilet.

Newsweek subsequently retracted the report, saying its government source had indicated doubts about his information after publication.

The Bush administration blamed the report, at least in part, for deadly violence that erupted in Afghanistan and elsewhere in the Muslim world.

Human Rights Watch said that despite the Newsweek retraction it also had received reports from Muslim detainees -- at Guantanamo Bay, in Afghanistan and in Iraq -- that U.S. interrogators had repeatedly sought to offend their Islamic beliefs in order to humiliate them.

"Several detainees have alleged to Human Rights Watch and others that U.S. interrogators disrespected the Quran," according to a statement issued by the group Thursday.

Reed Brody, a spokesman for Human Rights Watch, noted the Newsweek story "would not have have resonated had it not been for the United States' extensive abuse of Muslim detainees and the government's failure to fully investigate all of those implicated."

The group also denied Newsweek's report caused the damage during last week's anti-American rioting in Afghanistan, blaming instead "violent protesters and poorly disciplined Afghan police and troops."

U.S. officials have acknowledged that investigations are ongoing into reports of religious intolerance -- including desecration of the Quran -- by interrogators at Guantanamo Bay.

"We do listen when people raise questions about the handling of the Quran, and we have made very clear what our policies are," Boucher said.

"The policy and practice that we follow at Guantanamo is to respect the religious rights of the prisoners."

"If there are credible instances that are called to our attention of where those rules were not followed or the policy is not carried out thoroughly, then we investigate," he said.